1. Field of the Invention
The present invention relates to a method of fabricating a conductive column, and more particularly to a method of fabricating a conductive column, which is adapted for fabricating a circuit board.
2. Description of Related Art
In semiconductor packaging process, circuit boards have been widely used due to their compatibility with complex circuit patterns, high integration and excellent performance. Circuit boards comprise patterned circuit layers and dielectric layers which are alternately deposited. For example, the method of forming circuit boards includes the laminating process and the build-up process. Regardless of the above mentioned methods, the patterned circuit layers are interconnected through conductive vias. The method of forming conductive vias includes conductive-through-via process, conductive-embedded-via process and conductive-blind-via process.
FIG. 1 is a cross sectional view showing a prior art circuit board with a plated through hole (PTH). The circuit board 100 comprises a dielectric layer 110 comprising a material such as epoxy resin or epoxy resin with glass fiber. A first conductive layer 120, comprised of, for example, a copper foil, is formed over a first surface 112 of the dielectric layer 110. A second conductive layer 130, comprised of, for example, a copper foil, is formed over a second surface 114 of the dielectric layer 110 opposite to the first surface 112. In order to electrically connect the first conductive layer 120 with the second conductive layer 130 through the dielectric layer 110, a plating-through-hole process is carried out. In the plating-through-hole process, a through hole 102 is formed in the dielectric layer 110, the first conductive layer 120 and the second conductive layer 130 by using a drilling process. An plating process is carried out to deposit a conductive material on the sidewalls of the through hole 102 and the surfaces of the first conductive layer 120 and the second conductive layer 130 so as to form an plating layer 140. Accordingly, the conductive via 142 of the plating layer 140 formed on the sidewalls of the through hole 102 electrically connects the first conductive layer 120 with the second conductive layer 130. Thereafter, downstream processes can be carried out to complete the fabrication of the circuit board 100.
In addition to the plating-through-hole process, a plating-filling-hole process can be further carried out to fill the through hole with a conductive material so as to form a conductive column, which can enhance heat dissipation of the circuit board. FIG. 2A is a cross sectional view showing another prior art circuit board with a conductive column, which is similar to the prior art described above, except that at least one through hole 202 is formed in the dielectric layer 210, a first conductive layer 220 and a second conductive layer 230 by using a drilling process, and then an plating process is carried out to deposit a conductive material on the sidewalls of the through hole 202 and the surfaces of the first conductive layer 220 and the second conductive layer 230 to form the plating layer 240, wherein the plating layer 240 fills the through hole 202 to form a conductive column 242. Compared with the conductive via 142 of the plating layer 140 in the through hole 102 in FIG. 1, the conductive column 242 in FIG. 2A has a greater heat dissipation area which improves heat dissipation of the circuit board 200a. 
FIG. 2B is a cross sectional view showing a prior art circuit board with a defective conductive column. During the plating-filling-hole process, the point discharging phenomenon occurs at two sharp edges of the through hole 202. It is believed that the point discharging phenomenon at the sharp edge 220a of the first conductive layer 220 and the sharp edge 230a of the second conductive layer 230 is most likely due to larger point discharge currents. The larger currents cause the conductive material to deposit faster on the sharp edge 220a of the first conductive layer 220 and the sharp edge 230a of the second conductive layer 230, and the conductive material deposited on the sharp edge 220a of the first conductive layer 220 and the sharp edge 230a of the second conductive layer 230 extend towards the center of the through hole 202. As a result, a void 242a is easily formed in the conductive column 242 formed in the through hole 202. The void 242a reduces the heat dissipation area of the conductive column 242. Accordingly, the heat dissipation of the circuit board 200b is lower than that of the circuit board 200a in FIG. 2A.